Method for redundancy backup of signaling link in IP network

ABSTRACT

The invention discloses a method for implementing signaling link redundancy in IP networks. Two ASPs are created for the same AS in the host at the IP network side, and all user adaptation protocols share ASPSM and ASPTM messages so that the states of the two ASPs can become active and inactive respectively, thus to implement two signaling links for serving the same traffic. When switch is initiated, SCTP association can be closed by using “graceful close”, and the SCTP itself will make sure to send out all the data remaining in its buffer and its higher-layer applications will also send subsequent data in order after learning the remaining data are all sent out, thus sequential delivery for the data can be guaranteed. This method can avoid data loss and disorder, and the speed for switch can be ensured because the backup link will be notified immediately after the data on the primary link are sent out.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Patent Application correspondingto PCT Pat. application No. PCT/CN02100854 filed on Nov. 28, 2002, whichclaims priority from Chinese Patent Application No. 01139026.3 filed onNov. 30, 2001.

FIELD OF THE INVENTION

The present invention relates generally to a method for accurate datadelivery between IP networks and conventional telecommunicationnetworks, and more particularly, to a method for implementing signalinglink redundancy in IP networks.

BACKGROUND OF THE INVENTION

In order to transit smoothly from conventional telecommunicationnetworks to next-generation IP networks, IETF (Internet Engineering TaskForce) proposes a set of signaling transport (SIGTRAN) protocol model,for adapting various signaling messages in conventionaltelecommunication networks into IP networks, herein adaptingspecifically means replacing the previous information exchanges(including primitive, message and etc) between software modules puttogether with standard protocol so that two software modules can beseparated completely without making modification. As shown in FIG. 1,signaling in conventional telecommunication network includes SS7(Signaling System 7), DSS1 (Digital Subscriber Signaling System No.1),V5 Signaling, SCCP (Signaling Connection Control Part) and etc. All ofthese protocols take SCTP/IP as their lower-layer carrier protocol. Fordifferent signaling, the signaling messages can be transferred over IPnetworks by using different adaptation protocols according to practicalrequirements, and the carried signaling is setting on top of theadaptation protocol. The signaling data and command packet will beconverted into corresponding adaptation protocol packet, and then betransferred to the destination in IP network via SCTP.

In this model, the SG (Signaling Gateway) on the border betweenconventional telecommunication network and IP network is responsible forconversion between signaling messages and IP packets. When there is anymessage to be transferred to SoftSwitch or MGC (Media GatewayController) in the SEP, the SEP (Signaling End Point) first sends themessage to the SG through the signaling link between the SEP and the SGUpon receipt of the signaling message from its peer, the signalingcarrier module in the SG reports it to the higher-layer via the internalinterface, and meanwhile a fake higher-layer user module converts thesignaling message into the corresponding different UA(User Adaptation)message according to the corresponding data and then sends UA message tothe corresponding SoftSwitch or MGC over the established SCTP (StreamControl Transfer Protocol) connection. The UA module in the SoftSwitchor MGC recovers the received message and notifies it to the userapplications of the higher layer through the internal interface, thusthe signaling message is transferred from conventional telecommunicationnetwork to IP network. Contrarily, when the ISUP (ISDN User Part) or TUP(Telephone User Part) module in the Softswitch or MGC has any message tobe transferred to the SEP in conventional telecommunication network, themessage will be delivered to the UA module through the internalinterface, and further transferred to the SG via SCTP. After obtainingthe message received by the UA module, the fake high-layer user modulein the SG sends it to the signaling carrier module in the SG through thesame internal interface. Ultimately, the message arrives at the SEPthrough the signaling link between the SG and the SEP, and thus thetransfer to conventional telecommunication network from IP network isachieved.

To adapt various signaling transfer into the new topologies in IPnetwork, SIGTRAN protocols group introduces the notion of AS(Application Server) and ASP (Application Server Process) for alladaptation protocols. AS represents the collection of some specificsignaling messages with advantage at shielding the difference insignaling ways, while ASP represents the process instance for handlingthe signaling message represented by the AS running on the SoftSwitch orMGC. After receiving a signaling message, the SG finds the AS to whichthe SG belongs according to the characteristics value carried in themessage, then finds the available ASP according to the AS, and finallyencapsulates the signaling message into IP packet and sends it to theSoftSwitch or MGC to which the ASP is pertained. Thus, signaling messagedistribution from signaling network to IP network is accomplished. An AScan be handled by one ASP, or by several ASPs simultaneously to achieveload share.

All adaptation protocol messages have ASPSM (Application Server ProcessState Maintenance) and ASPTM (Application Server Process TrafficMaintenance) messages with the same function, and the two messages arefor implementing signaling link in IP networks. In addition, alladaptation protocols have SCTP as their carrier protocol. Therefore, allkinds of signaling links can utilize the same technique to realizeredundancy.

There have been some discussions and considerations for link redundancyin current protocols, and the physical model is illustrated in FIG. 7.Every SG can connect several MGCs and every MGC can connect several SGstoo. For those traffics that belong to the same AS, the SG can hand themto several MGCs for handling respectively according to the specificredundancy rule. The traffic messages of the same MGC can also be handedto different SGs for delivery according to the specific redundancy rule.Thus, it can be seen that the redundancy considered in the protocol isbased on the whole network topology in such a basic way that tworeliable connections are established respectively as the primary andbackup links. In normal condition, the connection of the primary link isfor data transmission and reception while the backup data is not fordata transmission and reception. When a device has malfunction ordoesn't work properly, all traffics will be handled by the backup link.Since different connections over IP networks are very likely to traverseacross different networks, there can be great difference between thetransfer rate of the primary link and that of the backup link. Duringswitch, the late transmitted data may arrive earlier, which can lead todata disorder and loss. Under this situation, the protocol has not yetoffered a good solution to avoid the data loss and disorder duringswitch.

SUMMARY OF THE INVENTION

The present invention aims at effectively avoiding data disorder andloss during switch between the primary and backup links in SIGTRANprotocol and proposes a method for implementing signaling linkredundancy based on SIGTRAN adaptation model.

To achieve the above object, the method for implementing signaling linkredundancy in IP networks comprises:

-   -   (1) the ASPs corresponding to the two links are configured in        the host at the IP network side, and the two ASPs establish SCTP        association with the SG respectively after startup;    -   (2) after SCTP association is established successfully, ASP        startup messages are sent to the UA modules of the two ASPs        respectively;    -   (3) after receiving the ASP startup ACK message from the SG, the        UA module of the primary link sends ASP ACTIVE message, whereas        the backup link is inactive without transmission and reception        of signaling messages;    -   (4) the UA module of the primary link enters into active state        after receiving the ASP ACTIVE ACK message, while the UA module        of the backup link keeps inactive;    -   (5) when switch is required to initiate, the UA module of the        primary link at the side requesting for switch sends a request        for “graceful close” the primary link to the SCTP carrier module        in the lower layer;    -   (6) after the “graceful close” is successful, the UA module of        the backup link sends ASP ACTIVE message, and the backup link        starts data transmission and reception;    -   (7) if the above “graceful close” request in step (5) is not        successful, mandatory switch will be performed.

In the above method, step (5) can also comprise: when switch between theprimary and backup links is required to initiate, setting a switchtiming so that mandatory switch can be performed if the preset switchtiming expires and the request for “graceful close” is not accomplishedyet.

In the proposed method, two ASPs are created for the same AS in the hostat the IP network side, and all user adaptation protocols share ASPSMand ASPTM messages so that the states of the two ASPs can become activeand inactive respectively, thus to implement two signaling links forserving the same traffic. When switch is carried out, SCTP associationcan use “graceful close”, and the SCTP itself will make sure to send outall the data remaining in its buffer and the applications on the SCTPwill also send subsequent data in order after learning the remainingdata are all sent out, thus sequential delivery for the data can beguaranteed. This method can avoid data loss and disorder, and the speedfor switch can be ensured because the backup link will be notifiedimmediately after the data on the primary link are sent out.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 illustrates the model for adapting each signaling of conventionaltelecommunication networks into IP networks proposed by IETF;

FIG. 2 illustrates the model for adapting #7 signaling from SS7 networkinto IP network through M3UA (MTP 3 User Adaptation Layer) proposed byIETF;

FIG. 3 illustrates the model for adapting #7 signaling from SS7 networkinto IP network through M2UA (MTP 2 User Adaptation Layer) proposed byIETF;

FIG. 4, FIG. 5 and FIG. 6 respectively represent the adaptation modelsfor V5 protocol, ISDN protocol and SCCP protocol proposed by IETF;

FIG. 7 illustrates the physical architecture of the SIGTRANprimary/backup link redundancy proposed by IETF;

FIG. 8 and FIG. 9 are flowcharts illustrating the switch initiated byMGC and SG respectively when utilizing the method of the presentinvention, by exemplifying data exchange between SS7 network and IPnetwork;

FIG. 10 depicts the physical model for implementing the method of thepresent invention in a MGC;

FIG. 11 depicts the physical model for implementing the method of thepresent invention between multiple MGCs.

DETAILED DESCRIPTION OF THE INVENTION

Detailed description of the proposed method will be given below, inconjunction with accompanying drawings and embodiments.

FIG. 1 has been explained before and won't be elaborated any moreherein. FIG. 2 to FIG. 6 illustrate the physical layer and signalingprotocols involved in adapting various signaling messages ofconventional telecommunication networks into IP networks. It can be seenthat all protocols have the common ground of taking SCTP/IP as theirlower-layer carrier protocol. Different signaling can use differentadaptation protocols according to practical requirement. For instance,in FIG. 2, #7 signaling adopts M3UA adaptation protocol, wherein SEPrepresents Signaling End Point, ISUP represents ISDN User Part, TUPrepresents Telephone User Part, MTP3 represents Message Transfer PartLevel 3, MTP2 represents Message Transfer Part Level 2, L1 representsMessage Transfer Part Level 1, NIF represents Nodal InterworkingFunction, M3UA represents MTP3 User Adaptation Layer, SCTP representsStream Control Transmission Protocol, SG represents Signaling Gateway,MGC represents Media Gateway Controller and SoftSwitch represents softswitch. In FIG. 3, #7 signaling adopts M2UA protocol, wherein SEPrepresents Signaling End Point, MTP3 represents Message Transfer PartLevel 3, MTP2 represents Message Transfer Part Level 2, L1 representsMessage Transfer Part Level 1, NIF represents Nodal InterworkingFunction, M2UA represents MTP2 User Adaptation Layer, SCTP representsStream Control Transmission Protocol, SG represents Signaling Gateway,MGC represents Media Gateway Controller and SoftSwitch represents softswitch. In FIG. 4, V5 signaling adopts V5UA adaptation protocol, whereinAN represents Access Network, LAPV5 represents Link Access Process forV5 link, NIF represents Nodal Interworking Function, V5UA represents V5User Adaptation Layer, SCTP represents Stream Control TransmissionProtocol, SG represents Signaling Gateway, MGC represents Media GatewayController and SoftSwitch represents soft switch. In FIG. 5, ISDN adoptsIUA adaptation protocol, wherein EP represents ISDN End Point, NIFrepresents Nodal Interworking Function, IUA represents ISDN UserAdaptation Layer, SCTP represents Stream Control Transmission Protocol,SG represents Signaling Gateway, MGC represents Media Gateway Controllerand SoftSwitch represents soft switch. In FIG. 6, SCCP signaling adoptsSUA adaptation protocol, wherein SEP represents Signaling End Point,SCCP represents Signaling Connection Control Part, SUAP represents theHigher-layer User Part of SCCP, MTP3 represents Message Transfer PartLevel 3, MTP2 represents Message Transfer Part Level 2, L1 representsMessage Transfer Part Level 1, NIF represents Nodal InterworkingFunction, SUA represents SCCP User Adaptation Layer, SCTP representsStream Control Transmission Protocol, SG represents Signaling Gateway,MGC represents Media Gateway Controller and SoftSwitch represents softswitch. Above the adaptation protocol, there are the carried signalingdata and command packet. Signaling data and command packet are convertedinto the corresponding adaptation protocol packets, and then deliveredto the destination in IP networks by using SCTP.

The method will be described below, by taking an example where dataexchange occurs between SS7 network and IP network. The host at the IPnetwork side can be MGC or SoftSwitch system, and we take the MGC as anexample here. The ASPs corresponding to the two links are configured inthe MGC and the two ASPs establish SCTP association with the SGrespectively after startup. After SCTP association is established, ASPstartup messages are sent to the UA modules of the two ASPsrespectively. On receipt of the ASP startup ACK message from the SG, theUA module of the primary link sends ASP ACTIVE message, where thetraffic mode in the message is override, whereas the backup link isinactive without transmission and reception of signaling messages. TheUA module of the primary link enters into active state on receipt of theASP ACTIVE ACK message, while the UA module of the backup link keepsinactive. When switch is required to initiate, the UA module of theprimary link at the side requesting for switching sends request for“graceful close” the primary link to the SCTP carrier module of thelower-layer. To avoid failure of “grace close” caused by the anomaly ofthe lower-layer carrier state or network, a switch timing can be setwhen the switch is initiated so that mandatory switch will be performedif the switch time expires and the request for “graceful close” is notaccomplished yet.

Both ends (SG and MGC or SoftSwitch) of a signaling link in IP networkscan initiate switch request. The mechanism is the same for the twocases, but there can be of some slight differences in operations sincethe two ends are not peers.

As FIG. 8 shows, when the MGC initiates switch for the primary/backuplinks, the UA module of the primary link first sends “graceful close”request to the SCTP carrier module of the lower-layer, pauses datatransmission and buffers the subsequent data at the same time. Asspecified in the protocol, SCTP stops receiving higher-layer data onreceipt of the “graceful close” request from higher-layer and sends aSHUTDOWN message to its peer after sending out all of the data packetsin its sending buffer. Meanwhile SCTP notifies the UA module so that thelatter can learn the data requested for transmission have been sent out.The UA module of the backup link sends ASP activation message to the SGimmediately after knowing the SHUTDOWN message of the primary link hasbeen sent out, wherein the traffic mode is override. As specified in theprotocol, on receipt of the activation message (override mode) from thebackup link, the SG will take this ASP as the primary ASP of the AS,i.e. the subsequent No.7 messages will be distributed to this ASP and atthe same time ASP ACTIVE ACK message will be sent to the MGC. Afterreceiving the ASP ACTIVE ACK message from the SG, the backup link canonly send data out but not receive data for now if the “graceful close”procedure of the primary link is not finished yet. After the primarylink accomplishes “graceful close” procedure, the backup link cantransmit and receive data.

Referring to FIG. 9, when the SG initiates primary/backup switch, the UAmodule at the SG side requests for “graceful close” the connection ofthe primary link, and stores the data to be transmitted in its buffertemporarily. After sending out the data in the buffer, the SCTP sends aSHUTDOWN message to its peer as specified in the protocol. Afterreceiving the SHUTDOWN message, the SCTP of the primary link in the MGCnotifies the higher-layer UA module. After learning the SHUTDOWN messagereceived by the SCTP, the UA module of the primary link stops datatransmission over the primary link and the UA module of the backup linkimmediately sends ASP ACTIVE message, where the traffic mode isoverride. On receipt of the ASP ACTIVE ACK message from the SG, if the“graceful close” procedure of the primary link is not finished yet, thebackup link can only receive data and not send data out temporarily.After the primary link accomplishes “graceful close” procedure, thebackup link can receive and transmit data.

If the primary link can't accomplish “graceful close” due tomalfunction, the backup link can be activated to override the formerprimary link, but transmission of the above data should be delayed for awhile to guarantee the message sequence as much as possible.

FIG. 10 shows the redundancy model put forward based on the method ofthe present invention. Two ASPs are configured in a MGC, denoted as ASP1and ASP2 respectively, and they serve the same AS, i.e. process the samesignaling messages. In general, the two ASPs are located on differentprocessing boards, while they can also be located on the same processingboard.

The present invention can also be extended in such a way that theprimary and backup signaling links are implemented between multipleMGCs, as shown in FIG. 11, where ASP1 is established in MGC1 and ASP2 inMGC2. In this case, reliable transport protocols are needed for messageinteraction and data transfer between two hosts. In addition, to realizebetter control, a management host can be added for primary/backupmanagement.

1. A method for implementing signaling link redundancy in IP networks,comprising: the ASPs (Application Server Process) corresponding to thetwo links are configured in the host at the IP network side, and thesaid two ASPs establish SCTP (Stream Control Transfer Protocol)association with the SG (Signaling Gateway) respectively after startup;after SCTP association is established successfully, sending ASP startupmessages to the UA(User Adaptation) modules of the two ASPsrespectively; after receiving the ASP startup ACK message from the SG,the UA module of the primary link sends ASP ACTIVE message, whereas thebackup link is inactive without transmission and reception of signalingmessages; the UA module of the primary link enters into active stateafter receiving the ASP ACTIVE ACK, while the UA module of the backuplink keeps inactive; when switch is required to initiate, the UA moduleof the primary link requesting for switch sends a request for “gracefulclose” the primary link to the SCTP carrier module in the lower layer;“graceful close” the primary link; after the “graceful close” issuccessful, the UA module of the backup link sends ASP activationmessage, and the backup link starts data transmission and reception; ifsaid “graceful close” is not successful, mandatory switch will beperformed.
 2. The method for implementing signaling link redundancy inIP networks according to claim 1, further comprising: when switchbetween the primary and backup links is required to initiate, setting aswitch timing so that mandatory switch can be performed if the presetswitch time expires and the request for “graceful close” is notaccomplished yet.
 3. The method for implementing signaling linkredundancy in IP networks according to claim 1 or 2, wherein when thehost at the IP network side initiates switch, the “graceful close” ofthe primary link further comprises: the UA module of the primary linkpauses data transmission and buffers subsequent data; the SCTP stopsreceiving higher-layer data on receipt of the “graceful close” requestfrom higher-layer, and sends a SHUTDOWN message to its peer aftersending out all the data packets in its sending buffer; the SCTPnotifies the UA module so that the latter knows the data requested fortransmission have all been sent out successfully; the UA module of thebackup link sends ASP activation message to the SG immediately afterknowing the SHUTDOWN message of the primary link has been sent out; onreceipt of the ACTIVE message from the backup link, the SG takes thisASP as the primary ASP of the AS, and at the same time sends ASP ACTIVEACK message to the host at the IP network side; during the “gracefulclose” procedure of the primary link, the backup link can only send dataout but not receive data temporarily.
 4. The method for implementingsignaling link redundancy in IP networks according to claim 1 or 2,wherein when the SG initiates switch, the “graceful close” of theprimary link further comprises: after initiating the requests for“graceful close” the primary link, the UA module at the SG side storesthe data to be transmitted in its buffer temporarily; after sending outthe data in the buffer, the SCTP sends a SHUTDOWN message to its peer;after receiving the SHUTDOWN message, the SCTP of the primary link atthe network side notifies its higher-layer UA module; after obtainingthe SHUTDOWN message received by SCTP, the UA module of the primary linkstops data transmission over the primary link and the UA module of thebackup link immediately sends ASP ACTIVE message; on receipt of the ASPACTIVE ACK message from the SG, if the “graceful close” procedure of theprimary link is not finished yet, the backup link can only receive dataand not send data out temporarily.
 5. The method for implementingsignaling link redundancy in IP networks according to claim 1 or 2,wherein said host at the IP network side can be MGC or SoftSwitch. 6.The method for implementing signaling link redundancy in IP networksaccording to claim 5, wherein said MGCs can be multiple, and there canalso be a management host for managing and controlling the primary andbackup links.